Human spinal disc prosthesis

ABSTRACT

The invention relates to a spinal disc endoprosthesis. The endoprosthesis has a resilient body formed of one or more materials which may vary in stiffness from a relatively stiff exterior annular gasket portion to a relatively supple central nucleus portion. Concaval-convex elements at least partly surround that nucleus portion so as to retain the nucleus portion and gasket between adjacent vertebral bodies in a patient&#39;s spine. Assemblies of endoprosthetic discs, endoprosthetic vertebral bodies, and endoprosthetic longitudinal ligaments may be constructed. To implant this endoprosthesis assembly, information is obtained regarding the size, shape, and nature of a patient&#39;s damaged spine. Thereafter, one or more prosthetic vertebral bodies and disc units are constructed in conformity with that information. Finally, the completed and conformed vertebral body and disc assembly is implanted in the patient&#39;s spine.

This is a continuation-in-part of U.S. patent application Ser. No.08/339,490, filed Nov. 14, 1994, which is abandoned.

BACKGROUND OF THE INVENTION

This invention relates generally to human prostheses, and especially tospinal column vertebral disc prostheses. The invention also relates tosurgical procedures for preparing the patient to receive a vertebraldisc endoprosthesis, and for implanting that endoprosthesis in thepatient's spine.

The herniation of a spinal disc and the often resultant symptoms ofintractable pain, weakness, sensory loss, incontinence and progressivearthritis are among the most common of debilitating processes affectingmankind. If a patient's condition does not improve after conservativetreatment, and if clear physical evidence of nerve root or spinal cordcompression is apparent, and if correlating radiographic studies (i.e.,MRI or CT imaging or myelography) confirm the condition, surgicalremoval of the herniated disc may be indicated. The process ofdiscectomy--as the name implies--involves the simple removal of the discwithout attempt to replace or repair the malfunctioning unit. In theUnited States in 1985, over 250,000 such operations were performed inthe lumbar spine and in the cervical spine.

Statistics suggest that present surgical techniques are likely to resultin short-term relief, but will not prevent the progressive deteriorationof the patient's condition in the long run. Through better pre-operativeprocedures and diagnostic studies, long-term patient results haveimproved somewhat. But it has become clear that unless the removed discis replaced or the spine is otherwise properly supported, furtherdegeneration of the patient's condition will almost certainly occur.

In the mid-1950's and 60's, Cloward and Smith & Robinson popularizedanterior surgical approaches to the cervical spine for the treatment ofcervical degenerative disc disease and related disorders of thevertebrae, spinal cord and nerve root; these surgeries involved discremoval followed by interbody fusion with a bone graft. It was noted byRobinson (Robinson, R. A.: The Results of Anterior Interbody Fusion ofthe Cervical Spine, J. Bone Joint Surg., 440A: 1569-1586, 1962) thatafter surgical fusion, osteophyte (bone spur) reabsorption at the fusedsegment might take place. However, it has become increasingly apparentthat unfused vertebral segments at the levels above and below the fusedsegment degenerate at accelerated rates as a direct result of thisfusion. This has led some surgeons to perform discectomy alone, withoutfusion, by a posterior approach in the neck of some patients. However,as has occurred in surgeries involving the lower back where discectomywithout fusion is more common as the initial treatment for discherniation syndromes, progressive degeneration at the level of discexcision is the rule rather than the exception. Premature degenerativedisc disease at the level above and below the excised disc can and doesoccur.

Spine surgery occasionally involves fusion of the spine segments. Inaddition to the problems created by disc herniation, traumatic,malignant, infectious and degenerative syndromes of the spine can betreated by fusion. Other procedures can include bone grafts and heavyduty metallic rods, hooks, plates and screws being appended to thepatient's anatomy; often they are rigidly and internally fixed. Noneprovide for a patient's return to near-normal functioning. Though theseprocedures may solve a short-term problem, they can cause other, longerterm, problems.

A number of attempts have been made to solve some of the problemsdescribed above by providing a patient with spinal disc prostheses, orartificial discs of one sort or another. For example, Steffee, U.S. Pat.No. 5,031,437, describes a spinal disc prosthesis having upper and lowerrigid flat plates and a flat elastomeric core sandwiched between theplates. Frey et al., U.S. Pat. Nos. 4,917,704 and 4,955,908, discloseintervertebral prostheses, but the prostheses are described as solidbodies.

U.S. Pat. Nos. 4,911,718 and 5,171,281 disclose resilient disc spacers,but no inter-connective or containing planes or like elements aresuggested, and sealing the entire unit is not taught.

It is the primary aim of the present invention to provide a vertebraldisc endoprosthesis which will perform effectively and efficientlywithin a patient's spine over a long period of time, and which will notencourage degeneration of or cause damage to adjacent natural discparts.

It is another object to provide a vertebral disc endoprosthesis whichdoes not require pins or other common mechanical hinge elements, yetwhich permits natural motion of the prosthetic parts and the adjacentnatural anatomy.

It is a related objective to provide a new vertebral disc endoprosthesissurgical procedure which will decrease post-operative recovery time andinhibit post-operative disc, vertebral body and spinal jointdegeneration.

It is yet another object to provide a method of installing theendoprosthesis so as to accurately mate the endoprosthesis with anadjacent specifically formed bone surface. An associated object is toprovide an endoprosthesis which will encourage bone attachment to, andgrowth upon, adjacent outer surfaces of the endoprosthesis.

Yet another object is to provide a vertebral endoprosthesis in which theparts are nononcogenic.

Still another object is to provide a vertebral disc endoprosthesishaving a resilient element to accommodate shocks and other forcesapplied to the spine.

Another object is to provide a highly effective vertebral endoprosthesiswhich includes several disc endoprostheses and one or more prostheticvertebral bodies. A related object is to provide these elements in apre-assembled array for implantation in a patient.

SUMMARY OF THE INVENTION

To accomplish these objects, the invention comprises a resilient bodyformed of a material varying in stiffness from a relatively stiffexterior portion to a relatively supple central portion. Aconcaval-convex means at least partly surrounds that resilient body soas to retain the resilient body between adjacent vertebral bodies of apatient's spine. If medical considerations so indicate, several discendoprostheses can be combined with one or more endoprosthetic vertebralbodies in an entire assembly.

To implant this endoprosthesis assembly, information is obtainedregarding the size, shape, and nature of a patient's damaged naturalspinal discs. If one or more of the patient's vertebral bodies alsorequire replacement, information about those bodies is also obtained.Thereafter, one or more prosthetic disc units and interposed prostheticvertebral body units are constructed and preassembled in conformity withthat information. Finally, the completed and conformed prosthetic discand vertebral body assembly is implanted in the patient's spine.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings. Throughout the drawings, like reference numerals refer to likeparts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary vertical view of a portion of a human spine inwhich is installed a novel vertebral disc endoprosthesis embodying thepresent invention;

FIG. 2 is a fragmentary side elevational view similar to FIG. 1 showingthe elements of a patient's spine and having a novel vertebral discendoprosthesis embodying the present invention installed therein;

FIG. 3 is a sectional view taken substantially in the plane of line 3--3in FIG. 1;

FIG. 4 is an exploded view of the novel vertebral disc endoprosthesis;

FIG. 5 is a vertical fragmentary view of a patient's spine similar toFIG. 1, but showing a series of novel disc endoprosthesis unitsinstalled in the spine and interconnected to one another;

FIG. 6 is a fragmentary sectional view of a patient's spine similar toFIG. 3 and taken along line 6--6 in FIG. 5, but showing a natural uppervertebral body, and upper endoprosthetic disc; an adjacentendoprosthetic vertebral body; a second or lower endoprosthetic disc;and a second or lower natural vertebral body;

FIG. 7 is a sectional view taken substantially in the plane of line 7--7of FIG. 6;

FIG. 8 is a fragmentary side elevational view of the assembly shown inFIG. 6; and

FIG. 9 is a fragment vertical view, similar to FIG. 1, of a portion of ahuman spine in which is installed a variant form of the novel vertebraldisc endoprosthesis the variant form having a prosthetic longitudinalligament;

FIG. 10 is a sectional view taken substantially in the plane of line10--10 in FIG. 9;

FIG. 11 is a top view of a retainer means for use with a vertebral discendoprosthesis;

FIG. 12 is a sectional view taken substantially in the plane of line12--12 of FIG. 11;

FIG. 13 is a side view of a vertebral disc endoprosthesis having agroove for receiving the retainer means; and

FIG. 14 is a cross-sectional view of the retainer means in use.

DETAILED DESCRIPTION

While the invention will be described in connection with a preferredembodiment and procedure, it will be understood that it is not intendedto limit the invention to this embodiment or procedure. On the contrary,it is intended to cover all alternatives, modifications, and equivalentsas may be included within the spirit and scope of the invention asdefined by the appended claims.

Turning more specifically to FIGS. 1-3, a portion of a human spine 10 isshown. The illustrated spine 10 has been subjected to a discectomysurgical process. To discourage degeneration of or damage to the naturalvertebral bodies 12 and 14 and their respective facet joints, inaccordance with the invention, a vertebral disc endoprosthesis 18 isaffixed between the adjacent natural vertebral bodies 12 and 14. Herethis vertebral disc endoprosthesis 18 comprises a resilient disc body 20having a relatively stiff annular gasket exterior portion 22 and arelatively supple nuclear central portion 24. The annular gasket 22 canbe formed from a suitable biocompatible elastomer of approximately 90durometer hardness and the nuclear central portion 24 can be formed froma softer biocompatible elastomeric polymer of approximately 30 durometerhardness.

Concaval-convex means 30 surround the resilient body 20 to retain theresilient body 20 between the adjacent natural vertebral bodies 12, 14in a patient's spine 10. To this end, as shown in FIG. 3, theconcaval-convex means 30 comprise two generally L-shaped supports 32 and34. The supports 32, 34 each have confronting first concaval-convex legs42, 44, each leg being of relatively constant cross-sectional thickness.Each leg 42, 44 has an outer convex surface 52, 54 for engaging theadjacent bone of the natural vertebral bodies 12, 14. Correspondinginner concave surfaces 62, 64 in confronting array retain the resilientbody 20 in its illustrated compressive force shock-absorbing position.These supports 32 and 34 can undergo principle movement away from oneanother, but only limited secondary translational, rotational anddistractional motion will occur. Each support 32, 34 has a second wingor leg 72, 74 extending generally perpendicularly to the first legs 42,44 respectively, and adapted for affixation to the adjacent bonestructure. To carry out aspects of the invention described below, thisaffixation is effectively accomplished by cannulated screw devices 82,84 which may be of a biodegradable type manufactured by Zimmer of Largo,Fla. Each device 82, 84 comprises a screw 92, 94; and a screw anchor102, 104 adapted to threadably receive the screw extends radially intoand seats within the bone structure 12, 14 as especially shown in FIG.3.

To discourage and prohibit migration of fluids between theendoprosthesis 18 and adjacent parts of the anatomy, a seal member 110is attached to the supports 32, 34 so as to surround the resilient body20 comprised of the gasket 22 and nucleus 24, in accordance with anotheraspect of the invention. Here, this seal member 110 comprises a flexiblesheet material having a multiplicity of pores. Preferably, the pores arefrom about 5 microns to about 60 microns in size. A flexible, strongpolymer sheet material from which this seal is formed can be aKevlar-like material, or it can be Goretex-like material, or otherappropriate biocompatible material, such as polyether, polyurethane, orpolycarbonate urethane membranes, can be used. Kevlar material isoffered by the E. I. DuPont de Nemours Company of Wilmington, Del. andGoretex material is offered by the W. T. Gore Company of Flagstaff andPhoenix, Ariz. Known sealing material can be applied to the flexiblesheet material so as to render the flexible sheet material substantiallyimpervious to the passage of any fluid. A watertight seal is perfectedwhen the seal 110 is glued or otherwise affixed to the legs 42, 44 andmediate portions of the legs 72, 74 as suggested in FIGS. 1-3.

In an alternative embodiment, the watertight seal between theendoprosthesis 18 and adjacent parts of the anatomy can be provided bydeveloping a groove 402 completely encircling the periphery of each ofthe legs 42, 44. Only one of the grooves is shown in FIG. 13. In thisembodiment, the seal member 410 is provided with a beaded edge 412 foreach groove. Additionally, a retaining band 415 is provided for eachgroove to retain the seal member 410 in grooves 402. The retaining bands415 can be in the form of a biocompatible monofilament wire of, forexample, stainless steel or titanium, a synthetic polymer cable or abraided wire cable. As shown in FIG. 11, each retaining band is crimpedanteriorly by a crimping sleeve 420. Of course, more than one crimpingsleeve may be used, if necessary. Although one sealing arrangementconsisting of the groove, beaded edge and retaining band is shown inFIG. 14, it should be understood that the sealing arrangement on theconcaval-convex leg of the other support is identical in design andfunction.

In use, the seal member 410 is placed about the concaval-convex means30. The retaining bands 415 are then placed adjacent to the respectivegroove 402 and crimped anteriorly, thereby fitting the bands into thegrooves. Each beaded edge 412 prevents the slipping of the seal memberunderneath the retaining band. Thus, the retaining band, the groove andthe beaded edge all cooperate to provide a water-tight seal to preventthe migration of fluids between the endoprosthesis 18 and adjacent partsof the anatomy. Glue can also be used to affix the seal member to theconcaval-convex means 30 as a supplemental means for perfecting theseal.

In accordance with another aspect of the invention, the supports 32, 34are formed of a biocompatible metal which may contain chromium cobalt ortitanium. Surface roughening or titanium beading 112, 114 on theexterior surfaces 52, 54 of legs 42, 44 encourages positive bondingbetween the adjacent bone and the convex surfaces 52, 54.

As suggested in FIGS. 9 and 10, a prosthetic longitudinal ligament 250can be connected between the screws 92, 94 to limit motions betweenelements of the spine 10 in the area where the endoprosthesis 18 isimplanted. This strap 250 may be made of the Kevlar-like material or theGoretex-like material described above, or it may be made of any otherstrong biocompatible material.

In accordance with another aspect of the invention, multipleendoprosthetic disc units can be placed in series with a straddlinginterlock appendage providing stability and fixation as shown in FIG. 5.Entire portions of a patient's spine can be replaced by a series ofinterconnected endoprosthetic vertebral bodies and endoprosthetic discunits. FIGS. 6-8 show an upper natural vertebral body unit 312 to whichan upper endoprosthetic body 308 has been attached. A lower naturalvertebral body 314 has attached, at its upper end, an endoprostheticdisc unit 318. Between these endoprosthetic disc units 308 and 318 is anendoprosthetic vertebral body 320. As suggested by FIG. 7, theendoprosthetic vertebral body 320 need not be irregularly shaped incross sectional aspect; rather, manufacturing processes may suggest thatit have a circular cross-sectional shape. As show in FIGS. 6 and 8, thisendoprosthetic vertebral body 320 comprises a titanium element 321, towhich are attached the preformed upper and lower endoprostheticvertebral body upper and lower concaval-convex elements 322, 324. Eachconcaval-convex element 322, 324 is attached to the prosthetic vertebralbody 320, as shown in FIG. 7, by extending set screws 330 through thetitanium vertebral body 321 into a stem-like projection 331 extendingfrom each of the concaval-convex elements 322, 324. A hole 360 in thebody 320 accommodates the stem-like projections 331 of theconcaval-convex elements 322 and 324. The stem-like projection 331 ofthe concaval-convex elements 322 and 324 is used only in conjunctionwith a prosthetic vertebral body implant construction 320.

An ear 340 is affixed, as by weldments 341, to a leg 342 extending froma concaval-convex element 322 as illustrated in FIGS. 6 and 8. An anchor352 can be threaded into the endoprosthetic vertebral body 320, and ascrew 362 can be turned into the anchor 352 so as to rigidly assemblethe leg 342 to a leg 354 extending from the lower endoprosthetic discunit 318.

The upper disc endoprosthesis 308, the endoprosthetic vertebral body320, and the lower disc endoprosthesis 318 can all be assembled andinterconnected as a unit before implantation in a patient's body whenindicated.

As also suggested in FIG. 6, the annular corners 372, 374 of naturalvertebral bodies 312, 314 each can extend irregularly radially outwardlyof the adjacent disc endoprosthesis 308, 318. However, the corners 382B,384B of the prosthetic vertebral body 320 do not generally extendsignificantly outside those disc units 308, 318, thus discouragingvertebral body engagement with and consequent abrasion or other damageto adjacent portions of the patient's natural anatomy. Preferably theendoprosthetic vertebral body 320 is not exactly right cylindrical inshape, but is rather slightly biconical; that is, the endoprostheticvertebral body 320 has a waist 390 of minimum radius R at an axialmedial point as suggested in FIG. 6.

According to yet another aspect of the invention, novel surgicalprocedures permit effective and permanent installation of theendoprosthetic vertebral body 320 and associated parts. First, a surgeonor medical technician develops information about the size, shape andnature of a patient's damaged vertebral body or bodies from radiographs,CT and/or MRI scans, noting specifically the anterior-posterior andlateral dimensions of the end plate of each involved vertebral body andthe vertical height of the anterior aspect of each involved vertebraland/or proximate vertebral body and vertical height of the mid portionof involved and proximate relatively normal intervertebral disc spaces.This information is transmitted by telephone, computer datalink ordocumentary transport to a specialized laboratory. That laboratoryconstructs one or more prosthetic assemblies of the sort shown in FIG. 6in conformity with the received information and this disclosure. Each ofthe assemblies can include a prosthetic vertebral body 321, and at eachbody end is a prosthetic disc 308, 318. Each prosthetic disc unitcomprises, in turn, the concaval-convex elements 30; the resilient body20 interposed between the concaval-convex elements; and the seal unit110 secured around the interior legs and resilient body. Thereafter, thecompleted and conformed assembly is implanted in the patient's spine 10.

When the unit or units have been received and the patient properlyprepared, the damaged natural spinal disc or discs and vertebral body orbodies are removed and the adjacent spinal bone surfaces are milled orotherwise formed to provide concave surfaces to receive the confrontingconvex surfaces 52, 54. Thereafter, the disc units and vertebral bodyare installed in the patient's spine.

To accurately locate the concaval-convex surfaces in the patient'sspine, holes 382A, 384A (FIG. 3) are precisely located and then formedin the bone structure using a measuring instrument centered in theevacuated natural intravertebral disc space. These holes are then tappedto form female threads therein. When the threads have been formed, theanchors 102, 104 are implanted in the respective tapped holes, therebycreating an imaginary platform of reference points located preciselywith respect to the patient's spine. After the holes have been formedand the anchors 102, 104 implanted, a bone surface milling jig (notshown) is affixed to the anchors 102, 104 and the desired concavesurfaces of predetermined shape are formed on the inferior and superiorsurfaces of the opposing vertebral bodies using one of a selection ofpredetermined milling head or bit sizes. Thereafter, the bone millingjig is removed and the concaval-convex elements 52, 54 identical inshape to the milled surfaces 112, 114 are inserted between thedistracted milled vertebral bodies 12, 14. The distraction device isthen moved. The concaval-convex structures are then attached by the sameanchors 102, 104 to the bone, thus insuring a precise and stable matebetween the bone surfaces and the convex surfaces 52, 54.

If necessary, a damaged implanted nucleus and/or gasket 24 can beremoved and replaced. This can be accomplished by slitting the seal 110;removing the annular gasket 24 and damaged nucleus 22, and replacingthem with new, undamaged elements. Thereafter, the seal 110 can bere-established by suturing or gluing closed the slit seal.

We claim:
 1. A vertebral disc endoprosthesis, comprising a resilientbody formed of materials varying in stiffness from a relatively stiffexterior portion to a relatively supple central portion; andconcaval-convex elements at least partly surrounding the resilient bodybetween adjacent vertebral bodies for retaining the resilient bodybetween adjacent vertebral bodies in a patient's spine, and wherein saidconcaval-convex elements each comprise generally L-shaped supports, eachsupport having a first concaval-convex leg, the first leg having anouter convex surface for engaging adjacent bone and a correspondinginner concave surface for retaining the resilient body, each supportfurther having a second leg extending generally perpendicularly to thefirst leg and adapted for affixation to adjacent bone structure.
 2. Avertebral disc endoprosthesis according to claim 1 wherein saidresilient body comprises an annular gasket and a nuclear centralportion.
 3. A vertebral disc endoprosthesis according to claim 1 furthercomprising cannulated screw means for attaching the concaval-convexelement supports to adjacent bone structure.
 4. A vertebral discendoprosthesis according to claim 3 wherein said cannulated screw meanscomprises a screw, and a screw anchor seatable within bone structure andadapted to threadably receive the screw.
 5. A vertebral discendoprosthesis according to claim 1 further comprising a seal memberattached to the concaval-convex elements and surrounding said resilientbody.
 6. A vertebral disc endoprosthesis according to claim 5 whereinsaid seal member comprises a flexible shell material having amultiplicity of pores, the pores being from about 5 microns to about 60microns in size.
 7. A vertebral disc endoprosthesis according to claim 6further including sealing means applied to said flexible sheet materialto render said flexible sheet material substantially impervious to thepassage of any fluid.
 8. A vertebral disc endoprosthesis according toclaim 5 wherein said concaval-convex elements and said seal membercollectively surround said resilient body with a watertight seal.
 9. Avertebral disc endoprosthesis according to claim 2 wherein said annulargasket is relatively stiff and said nuclear central portion isrelatively supple.
 10. A vertebral disc endoprosthesis according toclaim 1 wherein said concaval-convex elements are formed of abiocompatible metal.
 11. A vertebral disc endoprosthesis according toclaim 1 wherein said concaval-convex elements are formed of a metalcontaining titanium.
 12. A vertebral disc endoprosthesis according toclaim 1 wherein said concaval-convex elements are formed of a metalcontaining chromium cobalt.
 13. A vertebral disc endoprosthesisaccording to claim 10 wherein said concaval-convex elements are eachpartly defined by exterior surfaces, and wherein the endoprosthesisfurther includes metal beading on at least part of the exteriorconcaval-convex element surfaces for encouraging bonding between boneand said exterior concaval-convex element surfaces.
 14. A vertebral discendoprosthesis according to claim 1 wherein said concaval-convexelements are provided with roughened outer surfaces to encouragepositive bonding of bone to said concaval-convex element surfaces.
 15. Avertebral disc endoprosthesis according to claim 1 wherein saidconcaval-convex elements are formed of a non-oncogenic material.
 16. Thevertebral disc endoprosthesis according to claim 1 wherein eachconcaval-convex element is provided with a respective groove.
 17. Thevertebral disc endoprosthesis according to claim 16 further comprising aseal member including beaded edges, the seal member attached to theconcaval-convex elements and surrounding said resilient body.
 18. Thevertebral disc endoprosthesis according to claim 17 further comprisingretainer means for retaining the seal member against said grooves, theretainer means cooperating with the beaded edges and the grooves to forma watertight seal.
 19. The vertebral disc endoprosthesis according toclaim 18 wherein the retainer means can be in one of the followingforms: a biocompatible monofilament metal wire, a synthetic polymer bandor a braided wire cable.
 20. The vertebral disc endoprosthesis accordingto claim 19 wherein the biocompatible monofilament metal wire is formedof stainless steel or titanium.
 21. The vertebral disc endoprosthesisaccording to claim 18 further comprising a crimping means for crimpingthe retainer means about the seal member.
 22. The vertebral discendoprosthesis according to claim 1 wherein each support includes agroove about its circumference, the groove encircling the periphery ofthe first leg.
 23. A vertebral endoprosthesis comprising an integraldisc unit, said unit including a pair of confronting L-shaped supportshaving concaval-convex shapes in given legs, a resilient body interposedbetween the supports, and a flexible seal extending from one support tothe other and sealing the resilient body within the supports inside asubstantially watertight compartment.
 24. A vertebral endoprosthesisaccording to claim 23 further comprising a plurality of said integraldisc units.
 25. The vertebral endoprosthesis according to claim 23wherein each support includes a groove about its periphery and whereinthe seal includes beaded edges.
 26. The vertebral endoprosthesisaccording to claim 25 further comprising retainer means for retainingthe seal against said grooves, the retainer means cooperating with thebeaded edges and the grooves to form a watertight seal.
 27. Thevertebral endoprosthesis according to claim 26 wherein the retainermeans can be in one of the following forms: a biocompatible monofilamentmetal wire, a synthetic polymer band or a braided wire cable.
 28. Thevertebral endoprosthesis according to claim 27 wherein the biocompatiblemonofilament metal wire is formed of stainless steel or titanium. 29.The vertebral endoprosthesis according to claim 26 further comprising acrimping means for crimping the retainer means about the seal.
 30. Avertebral disc endoprosthesis comprising a resilient nucleus, rigidconcaval-convex elements at least partly surrounding the nucleus, anannular gasket ring surrounding the nucleus, and a seal member formed offlexible material and attached to the concaval-convex elements andsurrounding the nucleus and the annular gasket ring.
 31. A vertebraldisc endoprosthesis according to claim 30 wherein said concaval-convexelements each comprise generally L-shaped supports, each support havinga first concaval-convex leg, the first leg having an outer convexsurface for engaging adjacent bone and a corresponding inner concavesurface for retaining the nucleus, each support further having a secondleg extending generally perpendicularly to the first leg and adapted foraffixation to adjacent bone structure.
 32. A vertebral discendoprosthesis, according to claim 31 further including screw meansadapted for connection to said legs and for affixation in a generallyradial direction in adjacent generally cylindrical bone vertebrae. 33.The vertebral disc endoprosthesis according to claim 31 wherein eachsupport includes a groove about its circumference.
 34. A vertebral discendoprosthesis according to claim 30 further including means affixed tothe concaval-convex elements for encouraging bone growth partially uponand bone bonding with said concaval-convex elements.
 35. A vertebraldisc endoprosthesis according to claim 30 further including means forinterconnecting one of said concaval-convex elements to aconcaval-convex element of another vertebral disc endoprosthesis,thereby permitting the replacement of several natural vertebral discs.36. The vertebral disc endoprosthesis according to claim 30 wherein eachelement includes a respective groove and wherein the seal memberincludes beaded edges.
 37. The vertebral disc endoprosthesis accordingto claim 36 further comprising retainer means for retaining the sealmember against said grooves, the retainer means cooperating with thebeaded edges and the grooves to form a watertight seal.
 38. Thevertebral disc endoprosthesis according to claim 37 wherein the retainermeans can be in one of the following forms: a biocompatible monofilamentmetal wire, a synthetic polymer band or a braided wire cable.
 39. Thevertebral disc endoprosthesis according to claim 38 wherein thebiocompatible monofilament metal wire is formed of stainless steel ortitanium.
 40. The vertebral disc endoprosthesis according to claim 37further comprising a crimping means for crimping the retainer meansabout the seal member.
 41. A vertebral disc endoprosthesis comprising aresilient nucleus, first and second rigid concaval-convex elements atleast partly surrounding the nucleus, first and second legs formed,respectively, with the first and second rigid concaval-convex elements,first and second means for affixing the respective legs to vertebralbodies adjacent the concaval-convex elements and nucleus, andlongitudinal ligament prosthesis means extending between the legs of thefirst and second concaval-convex elements to inhibit undesirable motionof the vertebral bodies relative to one another.
 42. A vertebral discendoprosthesis comprising a rounded, resilient nucleus body convex onall surfaces and concaval-convex elements, each concaval-convex elementbeing of relatively constant cross-sectional thickness and having anouter convex surface for engaging adjacent bone structure which has beenmilled to mate with the concaval-convex element outer convex surface,and a corresponding inner concave surface for engaging the roundedresilient body, wherein said resilient nucleus body comprises arelatively resilient central body and a relatively stiff gasketsurrounding a circumference of the central body, the resilient nucleusbody snugly engaging the adjacent, mating concave surfaces of theconcaval-convex elements.
 43. A vertebral disc endoprosthesis accordingto claim 42 wherein the concaval-convex elements do not engage oneanother.